A fuel tank for a motor vehicle generally includes a fill tube through which fuel is added to the tank, and a vent tube through which displaced air and vapor exit the tank. In a typical refueling operation, fuel is supplied to the tank through a nozzle, which is designed to cut off the supply of fuel when the tank becomes full. To this end, the nozzle may include a pressure-actuated cut-off valve. The fuel tank may signal fullness by providing an increased internal pressure, which forces fuel up the fill tube to close the valve and cut off the supply of fuel. One way to achieve this is to provide, inside the tank, a vent tube with a substantially horizontal opening. The vent tube is positioned in the tank such that the horizontal opening is below the level of the fuel only when the tank is full. The other end of the vent tank is maintained at or near atmospheric pressure.
As fuel is admitted to the fuel tank, displaced air and vapor are relieved through the vent tube, keeping the pressure in the tank and fill tube only slightly above atmospheric pressure. However, when the fuel level rises to meet the horizontal opening of the vent tube, air and vapor can no longer exit the vent tube, and the incoming fuel causes an increase in the internal pressure of the tank and the fill tube. This pressure increase causes fuel to travel up the fill tube, where it is sensed by the nozzle, causing the flow of fuel to be cut off.
The configuration summarized above is effective at preventing catastrophic spillage of fuel during unattended refueling, but does not always result in an ideal refueling experience. In some cases, when the tank reaches the full level, the internal pressure in the fill tube rises so abruptly that fuel already in the fill tube is ejected back out through the fill tube. This event is called ‘spit-back’ if ejection occurs promptly when the tank reaches the full level, and ‘well-back’ if it occurs after some delay. Both events are undesirable, as they may result in fuel being spilled on a motorist or service-station attendant, or on the exterior of the vehicle. Furthermore, any discharge of fuel outside the vehicle is wasteful, and contributes to overall hydrocarbon emissions.
Ejection of fuel from the fill tube of a motor vehicle has been addressed previously. For example, U.S. Patent Application Publication Number 2004/0144444 discloses a vent tube for a motor-vehicle fuel tank that extends to a significant height outside the tank. The reference indicates that the abrupt pressure increase at the full level is reduced due to fuel flowing up the vent tube against an increasing head pressure. The inventors herein have determined, however, that this solution may not be sufficient for all motor-vehicle refueling scenarios, and may not be adaptable to all motor vehicles. In particular, the amount of pressure reduction realized in this approach may not be sufficient to completely prevent ejection of fuel from the fill tube, depending on refueling conditions. In addition, the extended length of the vent tube may cause fittability issues in some motor vehicles.
Accordingly, one embodiment of this disclosure provides a fuel tank having an interior space defined by a wall, a fill tube to admit fuel into the interior space, and a pressure-relief vent to discharge air and vapor from the interior space as the fuel is admitted. The pressure-relief vent includes a vent tube extending through the wall and downward into the interior space. The vent tube has a non-circular opening. Using a pressure-relief vent of this description, ejection of fuel from the fill tube can be prevented reliably under a wide range of refueling conditions, and without causing fittability issues.
The summary above is provided to introduce a selected part of this disclosure in simplified form, not to identify key or essential features. The claimed subject matter, defined by the claims, is limited neither to the content of this summary nor to implementations that address the problems or disadvantages noted herein.